Atmospheric testing is required for two distinct purposes: evaluation of the hazards of the permit space and verification that acceptable conditions exist for entry into that space.

A confined space is one that is large
enough to enter and perform assigned work
in; it has limited or restricted ways to enter
or exit the space; and it was not designed to
be occupied continuously by a worker.

Evaluation testing

The atmosphere within a confined space
must be tested using equipment that is
designed to detect the chemicals that may
be present at levels that are well below the
defined exposure limits. Evaluation testing
is done to:

determine what chemical hazards are or
may become present in the space's atmosphere,
and

identify what steps must be followed and
what conditions must be met to ensure
that atmospheric conditions are safe for a
worker to enter the space.

The testing results and the decisions about
what steps must be followed before entry
must be evaluated by, or reviewed by, a
technically qualified professional like an
OSHA consultation service, a certified
industrial hygienist, a registered safety
engineer, or a certified safety professional.
The technically qualified professional must
consider all of the serious hazards in his/her
evaluation or review.

A permit space is a confined space that has
one or more of the following features: it has
or may contain a hazardous atmosphere; it
contains a material that can engulf a person
who enters; it has an inside design that
could trap or asphyxiate a person who enters (inwardly converging walls, or a floor that slopes downward to a smaller section);
or it has any other serious safety or health
hazards.

Verification Testing

Before a permit space that may have a hazardous
atmosphere can be entered, the
atmosphere must be tested using the steps
identified on the permit (developed during
evaluation testing). Verification testing is
done to make sure that the chemical hazards
that may be present are below the levels
necessary for safe entry, and that they meet
the conditions identified on the permit. Test
the atmosphere in the following order: (1) for
oxygen, (2) for combustible gases, and then
(3) for toxic gases and vapors.2 The testing
results -- the actual test concentrations --
must be recorded on the permit near the levels
identified for safe entry.

Duration of Testing

For each test required on the permit, you
must allow enough time for the air from the
space to be drawn into the equipment and
for the sensor (or other detection device) to
react to the chemical if it is present. This is
considered the "minimum response time"
and it will be noted by the manufacturer in
the operator's manual. Be aware that you
will need to add time to this "minimum
response time" if you have attached hosing
or a probe extension to the inlet. The additional
time is needed to allow the air from
the different depths of the space to be pulled
into the equipment inlet.

Testing Conditions in Spaces that May
Have Layered Atmospheres

For permit spaces that are deep or have
areas leading away from the entry point, the
atmosphere may be layered or may be different
in remote areas. For these spaces, testing
must be done in the area surrounding
the worker, which is considered four (4) feet
in the direction of travel and to each side. If
a sample probe is used to do the testing, then the worker must move slowly enough so that testing is completed, keeping the
equipment "response time" in mind, before
he/she moves into the new area.

Retesting the Space During Entry or
Before Re-Entry

Test the permit space routinely to make sure
that the atmospheric conditions continue to
be safe for entry.3

This is one in a series of informational fact sheets highlighting OSHA programs, policies or standards. It does not impose any new compliance requirements. For a comprehensive list of compliance requirements of OSHA standards or regulations, refer to Title 29 of the Code of Federal Regulations. This information will be made available to sensory impaired individuals upon request. The voice phone is (202) 693-1999; teletypewriter (TTY) number: (877) 889-5627.

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